The present invention relates to an engine control apparatus, particularly to an improved engine control apparatus suitable to control accurately a ratio of air to fuel when a fuel pressure is varying.
In the prior art engine control apparatus, a ratio of air to fuel (hereinafter, abbreviated as an A/F ratio) is controlled by controlling the amount of fuel. The control of the fuel amount is performed by using a signal from an A/F ratio sensor, which is provided in an exhaust pipe for outputting a signal corresponding to a rich or lean state of the A/F ratio. The fuel amount is increased or decreased by carrying out the predetermined integration until the state of the A/F ratio changes from one to the other. Thereby, the average value of the A/F ratio of the engine is maintained at the target A/F ratio.
However, In such an A/F ratio control, there is possibility that the A/F ratio deviates temporarily from the target value when the fuel pressure is changed over.
In order to improve the above point, Japanese Patent Application Laid-Open No.6-58188 discloses such technique that the average of the A/F feedback coefficient is shifted to a lean side or rich side when the fuel pressure is changed over by a fuel pressure switching means.
However, in this prior art, the average of the A/F ratio is shifted before the operation of integration. Therefore, in case that variation of the fuel pressure continuously increases or decreases, or in case that it takes much time to change the fuel pressure because of intrinsic properties of a fuel pressure adjusting unit, there is a problem that excess corrections are made to the amount of fuel injection, and the variation of the A/F ration or the deterioration of emission is incurred.